Microwave phase shifter



y 1967 P. c. GOODMAN 3,323,081

MICROWAVE PHASE SHIFTER Filed April 8, 1963 VOLTAGE 36 SOURCE PHASESHIFT AT ZERO CHANGE IN PHASE SHIFT MAGNET'C F'ELD REMAINS CONSTANTPHASE SHIFT WHEN MAGNETIC FIELD OF PARTICULAR MAGNITUDE IS APPLIED Fig.4

INVENTOR.

I PAUL C.GO0DMAN BY My FREQUENCY (GIGACYCLES) ATTORNEY I I I I I I I I II I l I I 52 I I PHASE SHIFT (DEGREES) United States Patent DelawareFiled Apr. 8, 1963, Ser. No. 271,362 1 Claim. (Cl. 33331) This inventionrelates to an improved microwave phase shifter and more particularly, toan electrically variable ferrite core microwave phase shifter.

In coaxial transmission lines, it is often important to have a phaseshifter which, upon a change in its propagation constant, can produce aphase shift change which is substantially the same over a broadfrequency range and one in which the propagation constant can be changedeasily to vary the amount of phase shift change produced. Anotherrequirement of such phase shifters is that they provide reciprocaloperation, that is, they should provide substantially the same phaseshift in either direction of wave transmission through the line.

This invention relates to an improved microwave phase shifter whichprovides the above characteristics. In accordance with the invention, ahelical conductor or helix is wound on a cylindrical rod of ferritematerial. Preferably, the helical conductor is wound in such a way thatthe length of the conductor is constant when viewed at any giventransverse section of the ferrite rod.

The ferrite rod and the helix wound thereon are axially disposed withinan outer conductor. A biasing magnetic field is applied to the rod in adirection transverse to the rod and the magnetic field may be varied tochange the propagation constant of the line and the amount of phaseshift change produced. The symmetry provided by using a transversemagnetic field makes propagation characteristics of the helix completelyreciprocal.

An object of this invention is to provide an improved microwave phaseshifter which comprises a rod of ferrite material upon which is wound ahelical conductor.

Another object of this invention is to provide a phase shifter of theabove character having a transverse magnetic field which may be variedto change the propagation constant of the phase shifter.

Other objects and advantages will become apparent from the followingdescription and from the appended drawings and claims.

In the drawings:

FIGURE 1 is a side view, partly in cross section and partly in schematicform, illustrating a phase shifter comprising an embodiment of thisinvention.

FIGURE 2 is an enlarged cross sectional view of the left end of thephase shifter shown in FIGURE 1.

FIGURE 3 is a section taken at substantially line 3--3 shown in FIGURE1.

FIGURE 4 is a graph showing the characteristics of the present phaseshifter.

In FIGURE 1 a ferrite rod 10, made of a material such as yttrium irongarnet with gadolinium substituted for part of the yttrium, is axiallydisposed within an outer conductor 12 made of a conductive material suchas brass.

A conductor 14 made of a material such as brass is wound on the rod 10.Between the axial positions 16 and 18, the conductor 14 is a helix 19and from these positions to the ends of the conductor, the conductor isa continuous tube. Preferably, the helix 19 is wound on the rod suchthat the length of the helix is constant when viewed at any giventransverse section of the rod 10. For example, in the transverse sectionshown in FIGURE 3, the length of the helix portion 20 is maintainedconstant throughout the helix 19 between the axial positions 16 and 18to obtain best results. In one phase shifter that was built, this lengthwas maintained constant at .35 inch, using a ferrite rod having adiameter of .20 inch.

A helical section 22 of larger pitch than the rest of the helix 19 and ahelical section 24 of still larger pitch are provided at the oppositeends of the helix to act as two section quarter-wave transformers tomatch the pres ent phase shifter to the coaxial transmission line intowhich it is to be inserted.

Annular members 26 (only one shown in FIGURE 2) made of a material suchas brass are disposed in contact with the opposite ends of the rod 10and the tubular portions of the conductor 14 extend over the members 26in electrical contact therewith. Screwed into the members 26 are prongedcenter conductors 28 for making contact with the center conductor of thecoaxial line in which the present phase shifter will be inserted.Annular spacers 30 made of an insulating material as Teflon are insertedinto the opposite ends of the conductor 12 over the conductors 28 tomaintain the spacing and axial position of the rod 10 and the conductor14 within the conductor 12.

A pair of pole pieces 32 and 34 of an electromagnet are positioned onopposite sides of the conductor 12 to apply a biasing magnetic field tothe rod 10. This magnetic field is provided in the air gap between thepole pieces and is dis-posed in a direction transverse to the rod 10.Suitable path means of high permeability (not shown) are connectedbetween the pole pieces 32 and 34 externally of the conductor 12 tocomplete the magnetic circuit. A variable direct voltage source 36 isconnected to the input of the electromagnet to obtain a magnetic fieldof a desired amount and direction. The pole pieces 32 and 34 are spaceda sufiicient distance from the ferrite rod 10 to provide a uniform fieldfor the rod and to provide a large air gap between the pole pieces andthe rod.

The phase shifter described above may be inserted into a standardcoaxial transmission line with standard coaxial connectors (not shown).When so inserted, the center conductors 28 will make electrical contactwith the center conductor of the coaxial line and the outer conductor 12will make electrical contact with the outer conductor of the coaxialline.

In a phase shifter of the above type that was built and designed for 3.3gigacycle operation, it was found that the phase shifter operatedsatisfactorily, providing a phase shift change that remainedsubstantially constant from 3 to 3.6 gigacycles, that is, a range of20%. This is shown in the graph of FIGURE 4. Line 50 is a plot of thephase shift produced by the phase shifter as a function of frequencywhen the magnetic field applied thereto is zero. Line 52 is a plot ofthe phase shift when a magnetic field of particular magnitude is appliedin a transverse direction to the ferrite rod. It will be noted thatbetween the lines 50 and 52, the phase shift change or differenceremains substantially constant over the range from 3 to 3.6 gigacycles,that is, the phase shift change is substantially independent offrequency in this range. If the magnetic field is increased, thisfurther reduces the propagation constant of the phase shifter and thetotal phase shift produced is correspondingly reduced. However, thephase shift change with respect to the total phase shift produced at amagnetic field of lower magnitude would remain substantially constantover the range from 3 to 3.6 gigacycles.

Another advantage of the phase shifter is that it has excellentreciprocal operation, that is, it will produce essentially the sameamount of phase shift regardless of which direction a Wave istransmitted through the coaxial line. This results because the magneticfield is applied in a transverse direction rather than in a longitudinaldirection as is the case in certain presently known phase shifters.Also, hysteresis effects in rod 10 are substantially eliminated becauseof the transverse field and because of the large air gap providedbetween the pole pieces 32 and 34 and the rod.

Although this invention has been disclosed and illustrated withreference to particular applications, the principles involved aresusceptible of numerous other applications Which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claim.

Having thus described my invention, I claim:

A microwave phase shifter for a coaxial transmission line comprising aconductive tubular outer member for connecting with the outer conductorof the coaxial line,

a ferrite member disposed axially within the outer member,

a conductive helix Wound on the ferrite member,

means for connecting the 'helix in series with the inner conductor ofthe coaxial line,

the helix having an increased pitch at both ends to match the phaseshifter to the coaxial line,

and means for applying a magnetic field to the ferrite member in adirection transverse to the axis of the member to provide for reciprocaloperation of the phase shifter,

the magnetic field being applied in the same direction through theferrite member,

the magnetic field being variable to control the magnitude of themagnetic field thereby controlling the amount of phase shift produced.

References Cited UNITED STATES PATENTS OTHER REFERENCES Scharfman:Ferrite Phase Shifters, Proc. I.R.E., vol. 44, pp. 1456-1459, October1956.

ELI LIEBERMAN, Primary Examiner.

C. BARAFF, Assistant Examiner.

